This invention relates to stable liquid biuret modified diphenylmethane diisocyanates which comprise a secondary amine based biuret modified diphenylmethane diisocyanate having an NCO group content of about 12 to about 30% by weight. The present invention also relates to stable liquid biuret allophanate modified MDIs, to stable liquid prepolymers of biuret modified MDIs, to stable liquid prepolymers of biuret allophanate modified MDIs, and to processes for the preparation of these compositions.
Modified isocyanates, including modified diphenylmethane diisocyanates are known and described in the art. Various modifications include, for example, allophanate modified, biuret modified, carbodiimide modified, isocyanurate modified, uretdione modified, urethane modified, oxadiainetrione modified and various combinations thereof.
Biuret modified diisocyanates including those based on diphenylmethane diisocyanate and prepolymers thereof, are known and described in, for example, U.S. Pat. Nos. 4,618,706, 4,677,136, 4,703,100, 4,837,359, 5,212,275, 5,428,124 and 5,994,491.
More specifically, U.S. Pat. Nos. 4,667,136 and 4,703,100 describe urea and/or biuret group containing polyisocyanates prepared by reacting an organic polyisocyanate and a high molecular weight (500 to 20,000) polyether or polyester containing at least two isocyanate-reactive groups which may be primary and/or secondary hydroxyl and/or amine groups and mixtures thereof, and optionally, a low molecular weight compound comprising one or more of aromatic diamines or triamines, (cyclo)aliphatic diamines of triamines, organic compounds containing at least one hydroxyl group and at least one amine group, organic compounds containing at least two alcoholic hydroxyl groups (and optionally an ether or ester group), and a hydrazine containing at least two reactive NH groups. Processes for the preparation of these urea and/or biuret modified isocyanates are also disclosed.
U.S. Pat. No. 4,837,359 discloses biurets prepared from a (cyclo)aliphatic diisocyanate and a (cyclo)aliphatic primary diamine compound. Biurets based on aromatic diisocyanates and diamines having aromatically attached amino groups and processes for their preparation are described by U.S. Pat. Nos. 4,618,706 and 5,994,491.
Urea and biuret prepolymers of diphenylmethane diisocyanates are known and described in U.S. Pat. Nos. 5,212,275 and 5,428,124. U.S. Pat. No. 5,212,275 describes liquid prepolymers of ureas and/or biurets prepared by reacting a polyfunctional secondary amine group containing compound corresponding to a specific structure with a polyisocyanate of the diphenylmethane series. Storage stable, liquid prepolymers of MDI containing urea and/or biuret groups are disclosed in U.S. Pat. No. 5,428,124. These are prepared by reacting an aminocrotonate with a mixture of MDI having a specified isomer distribution.
Allophanate modified diphenylmethane diisocyanates, prepolymers thereof, etc are known and described in, for example, U.S. Pat. Nos. 5,310,053 and 5,310,054. The liquid stable products of U.S. Pat. No. 5,319,053 are characterized by an NCO group content of 12 to 32.5%, and comprise the reaction product of an aliphatic alcohol and a specified mixture of isomers of diphenylmethane diisocyanate. This reference also discloses stable liquid MDI prepolymers which comprise the reaction product of the allophanate-modified MDI as described above, with an organic material containing two or more active hydrogen groups. U.S. Pat. No. 5,319,054 describes liquid allophanate modified MDI compositions which are storage stable at 25° C. The diphenylmethane diisocyanate has a specific isomer distribution requiring 2 to 60% by weight of 2,4′-diphenylmethane diisocyanate.
Allophanate modified diphenylmethane diisocyanate prepolymers are described in U.S. Pat. No. 5,440,003. These products are stable liquids at 25° C., and comprise the reaction product of an isomeric mixture of diphenylmethane diisocyanate and an aromatic alcohol such as phenol, with the resultant product being converted to the allophanate having an NCO group content of 12 to 32% by weight.
Advantages of the present invention include stable liquid products having unique structures and higher functionalities than other biuret modified isocyanates, biuret-allophanate modified isocyanates and prepolymers thereof. An additional advantage of the present invention includes a lower dimer content in the product since the conversion is performed at a low temperature (i.e. 50 to 110° C.) requiring a relatively short reaction time. Higher functionalities are expected to lead to faster cure rates in foams.